Field of the Invention
The present invention relates to an electrode material, an electrode, and a lithium ion battery. In particular, the invention relates to a cathode material for a battery, an electrode material which is suitably used for a cathode material for a lithium ion battery, an electrode including this electrode material, and a lithium ion battery including a cathode formed of this electrode.
Description of Related Art
Recently, as a battery in which a reduction in size and weight and an increase in capacity are expected, a non-aqueous electrolytic solution secondary battery such as a lithium ion battery has been proposed and has been
utilized in practice. A lithium ion battery includes a cathode and an anode which have a property capable of reversibly inserting and extracting lithium ions, and a non-aqueous electrolyte.
As an anode material and an anode active material of a lithium ion battery, a Li-containing metal oxide, such as a carbon-based material or lithium titanate (Li4Ti5O12), which has a property capable of reversibly inserting and extracting lithium ions is commonly used.
On the other hand, as a cathode material and a cathode active material of a lithium ion battery, an electrode material mixture including: a Li-containing metal oxide, such as lithium iron phosphate (LiFePO4), which has a property capable of reversibly inserting and extracting lithium ions; and a binder is used. By coating this electrode material mixture on a surface of a metal foil, known as a current collector, a cathode of a lithium ion battery is formed.
Such lithium ion batteries have a lighter weight, a smaller size, and higher energy than those of secondary batteries of the related art such as lead batteries, nickel-cadmium batteries, or nickel metal hydride batteries. Therefore, lithium ion batteries are used not only as a small-sized power supply for portable electronic equipment such as mobile phones or laptop PCs but as a stationary-type extremely-large-sized power supply.
In addition, recently, lithium ion batteries have been studied as a high-output power supply for plug-in hybrid vehicles, hybrid vehicles, electric tools, or the like. For a battery which is used as a high-output power supply, high-speed charge-discharge characteristics are required.
However, an electrode-active material, for example, an electrode material containing a lithium phosphate compound which has a property capable of reversibly inserting and extracting lithium ions has a problem of low electron conductivity. An electrode material is disclosed in which surfaces of electrode-active material particles are coated with an organic compound which is a carbon source in order to increase the electron conductivity of the electrode material, and the organic compound is carbonized. As a result, a carbon coating film is formed on the surface of the electrode-active material, and carbon in the carbon coating film is interposed between the electrode-active material particles as an electron conductive material (refer to Japanese Laid-Open Patent Publication No. 2001-15111).